Question

The time for half life of a first order reaction is 1 HR. What is the time taken for 87.5% completion of the reaction?

Answer 1

87.5 % means three half lives

As 87.5 %

1st half life = 50%

2nd half life = 50 + 50% (50) = 50 +25 = 75%

3rd half life = 50 + 50 % (50) + 50% (25) = 87.5%

Hence total time taken = 3 hours